Development of better anti Pneumocystis (Pc) drugs is needed. Humans and other mammals do not have the enzymes for producing C 24 alkylated or C 22 desaturated sterols, and when these compounds are present in the parasites, they represent putative "metabolic sterols" and "new" anti sterol drug targets. "Metabolic sterols" are those that have the precise stereochemical structural features required for proper functioning of the organism's membranes, and are particularly relevant to the development of chemotherapeutic agents against parasitic infections. Pneumocystis carinii appears to de novo synthesize isoprenoids. HMG CoA reductase activity was detected, and radiolabeled precursors were incorporated into P. carinii sterols, ubiquinones and other products. Ergosterol (the dominant sterol of "typical" fungi) was not detected in PC, but a number of delta 7C-24 alkylated sterols, similar to those found in some plants and in rust fungi, were identified. Pc was also found to have the ubiquinone (coenzyme Q) homologs, CoQ9and CoQ10; CoQ10was absent in the lung lipids of the rat host. Coenzyme Q is made of two parts, 1), the polyprenyl chain which varies in length, and is the basis for the designation of homologs, and 2) the aromatic moiety, which is made from dietary tyrosine in mammals, but is synthesized de novo in most plants, fungi and bacteria from chorismate, which is derived from the shikimate pathway (absent in mammals). The shikimate pathway leads to the formation of several other important metabolites, including aromatic amino acids, folate and Vitamin K. The project focuses on two novel targets, "metabolic sterols" and ubiquinone, especially those compounds that are present in Pc but absent in mammals. Included are studies on structural analyses employing a variety of chromatographic and mass spectral analyses. Biosynthetic pathways will be examined by metabolism of radiolabeled precursors. Also, sterol inhibitors with known specificity for a reaction will be utilized at low concentrations to cause the accumulation of precursors of the blocked reaction. Identification of the precursors will allow the elucidation of the biosynthetic pathway(s) functional in the organism.